1. Field of the Invention
The present invention relates generally to detecting circuit, and more particularly, to a circuit used for indicating process corner and extreme temperature.
2. Background
The circuits constructed on an IC chip or substrate is referred to as integrated circuits. Integrated circuits include transistors and resistors, for example. Integrated circuits are fabricated or manufactured in high volume using integrated circuit processes, such as a CMOS process. The integrated circuits may be characterized in terms of various circuit parameters, such as sheet-rho, transistor threshold voltage, and a transistor transconductance parameter, to name but a few.
The primary challenge in designing integrated circuits (IC) is to control circuit parameters, such as delay, in view of variations in the semiconductor fabrication process, supply voltage, and temperature. All of the above parameters and variables generally exhibit complex relationships among each other. Attaining homogeneous transistor operating parameters, such as threshold voltage and transconductance, within an integrated circuit is one of the most important, yet most difficult objectives for precision analog circuits. Transistor threshold voltage is also very critical in propagation speed for high speed low voltage digital circuits.
Process variations can cause unpredictable and undesired variations of the circuit parameters, which can adversely affect circuit performance. In other words, the circuit parameters tend to be process dependent. Thus, it is useful for a manufacturer to be able to quantify or determine the circuit parameters. Accordingly, there is a need to be able to measure and determine process-dependent circuit parameters associated with circuits constructed on an IC chip. A related need is to be able to determine a temperature of the IC chip and/or a power supply voltage of the IC chip.
U.S. Pat. No. 5,903,012, issued to David William Boerstler entitled “Process variation monitor for integrated circuits” discloses a current proportional to threshold voltage of MOS device. The circuit is shown in FIG. 1. Processing variation will cause the threshold voltage to be changed. However the threshold voltage also changed when temperature varies, including temperature effect we will be confused which one is the dominated factor.
U.S. Pat. No. 6,668,346, issued to Jurgen M. Schulz et al. entitled “Digital process monitor” discloses a ring oscillator is used for process detector. The circuit is shown in FIG. 2 However, temperature dependent oscillation frequency will also influence the counted result. User will be confused by process variation and temperature disturbance.
U.S. Pat. No. 7,449,908, issued to Lawrence M Burns et al. entitled “Process monitor for monitoring an integrated circuit chip” discloses by using varies of detector, the voltage signal then pass through a ADC for generating a digital codes is produced. The circuit is shown in FIG. 3. However, there are too much complex structure are used, which spends more layout area and calibration time. In additional, it needs an external off-chip accurate resistor to generate a constant current source, furthermore increases the BOM (Bill-of-material) of the product.